CAIRO (Reuters) - A Russian plane which crashed in Egypt last week was flying on auto-pilot and appeared to break up in mid-air after a sudden noise but it is too soon to conclude exactly what brought it down, the lead investigator said on Saturday.

Ayman al-Muqaddam, head of a team of experts looking into one of Egypt's worst air disasters, said the cockpit voice recording would be analysed to identify the nature of the noise, which Western governments have indicated may have been a bomb.

Islamic State militants fighting security forces in Egypt's Sinai Peninsula have said they brought down the Airbus A321, which crashed 23 minutes after taking off from the resort of Sharm al-Sheikh one week ago, killing all 224 passengers.

Fears that the crash was caused by Islamist militants led several Western countries, Russia and Turkey to suspend flights to Sharm al-Sheikh, stranding tens of thousands of holidaymakers and dealing a heavy blow to Egypt's vital tourist industry.

Muqaddam said the auto-pilot was still engaged when the crash occurred and debris were scattered over a wide area of the Sinai desert extending for 13 km (8 miles), adding that this was "consistent with an in-flight break-up".

The black boxes recovered from the crash site showed that a "a noise was heard in the last second of the ... recording". The recording will be send to a specialist laboratory for analysis.

Scientists have used such methods to examine the signature of dying cockpit recordings in aircraft bombings. Comparing the frequencies may help determine whether the sound recorded on the Russian jet comes from a deliberate or accidental explosion.

Muqaddam said his team, including experts from Egypt, Russia, France, Germany and Ireland, was considering "all possible scenarios for the cause of the accident" but had not yet reached any conclusion. He said structural fatigue, a fuel explosion and even lithium batteries carried by passengers could be a cause.

Referring to media reports that Western intelligence sources believe that the plane may have been brought down by a bomb, Muqaddam said no evidence related to those claims had been provided to his team.

ANGER AT WEST

His comments echoed the irritation expressed earlier on Saturday by Egypt's Foreign Minister Sameh Shoukry, who said that foreign intelligence about the cause of the crash had not been passed on to Cairo.

"The information we have heard about has not been shared with Egyptian security agencies in detail," Shoukry said. "We were expecting that the technical information would be provided to us."

He suggested countries now flagging the likelihood that militants were behind the crash should have heeded Egypt's repeated calls for coordination to combat terrorism.

"The spread of terrorism, which we have for a long time called on our partners to tackle more seriously, did not get through to many of the parties which are now exposed and which are currently working for the interests of their citizens to face this danger," he told a news conference.

Shoukry repeated his government's insistence that it was premature to reach conclusions, but security officials said they were checking video footage at Sharm al-Sheikh airport for any suspicious activity, in the clearest sign yet that they believe the Russian plane could have been deliberately targeted.

"We want to determine if, for instance, anyone sneaked past security officials or the metal detectors. We are also trying to determine if there was any unusual activity among policemen or airport staff," one of the officials told Reuters.

EXPLOSION

An Egyptian source close to the investigation of the Russian plane's black boxes said on Wednesday the cause of the crash was believed to be an explosion, but it was not clear whether that was the result of a bomb.

Western intelligence sources have said British and U.S. spies intercepted "chatter" from suspected militants suggesting that a bomb, possibly hidden in luggage in the hold, had downed the plane.

The Islamic State-affiliated Sinai Province, which claimed it brought the plane down, said it acted in revenge for Russian air strikes against Islamist fighters in Syria, where Islamic State controls large areas in the east and north of the country.

On Friday, Moscow suspended flights to Egypt, leaving nearly 80,000 Russians stranded, mainly in the Red Sea resorts of Hurghada and Sharm al-Sheikh, and adding to the growing chaos facing many tourists.

British attempts to fly home thousands of holidaymakers on Friday ran into trouble when Egypt restricted the number of flights, citing capacity at Sharm al-Sheikh airport and British airliners' refusal to take passenger luggage in the hold.

A British official at Sharm al-Sheikh airport said nine flights were expected to repatriate 2,000 stranded British tourists on Saturday, and the government hoped to get them all home within 10 days.

British media reported on Saturday that a British passenger jet came close to being hit by a rocket as it came in to land at Sharm al-Sheikh in August, although the British government said it had concluded the incident was part of routine Egyptian military exercises, not a deliberate attack.

The pilot of the Thomson flight from London to Egypt took evasive action after spotting the missile coming towards the plane as it flew to the Red Sea resort, the Daily Mail reported.